KIT – The Research University in the Helmholtz Association www.kit.edu
Institute for Applied Materials – Applied Materials Physics (IAM-AWP)
M. Rohde, C. Ziebert, H.J. Seifert
Safety studies on Li-ion cells with combined calorimetric and electrochemical methods
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP2
Thermal characterization and safety studies
Objective: Validated heat flow and temperature data for thermal management systems
www.techatplay.com
http://insideevs.com
→ Overheating
→ Overcharge
→ Overdischarge
→ Short Circuit
→ Accident
Possible Safety Impacts
Increasing scale
Thermal characterization
Accelerating Rate Calorimetry
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP3
Operating conditions: Lithium-ion batteries
Open circuit operation orstorage temperature < 80 °C
Operating temperature 30 – 40 °C
Charge / discharge between 0 – 60 °C
DT (Cell) < 10 K
DT (Pack: between cells) < 3 - 5 K
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP4
Heat generation in an electrochemical cell
S. Hallaj, H. Maleki, J.S. Hong, J.R. Selman, J. Power Sources 83 (1999) 1-8
∆𝐺 = −𝑛𝐹𝐸0
Gibbs Free Energy
∆𝑆 = 𝑛𝐹𝑑𝐸0
𝑑𝑇
Entropy change
𝑊𝑒𝑙 = 𝑛𝐹𝐸
Electric work
n number of electrons, Faraday constant F = 96485.3365 C/mol, E0 open circuit voltage (OCV), E voltage under load
𝑄 = ∆𝐺 + 𝑇∆𝑆 + 𝑊𝑒𝑙
ሶ𝑸𝒈 = −𝑰 𝑬𝟎 − 𝑬 − 𝑰𝑻𝒅𝑬𝟎𝒅𝑻
Parts of heat generation rate
1. “Reversible” heat rate caused bychemical reactions in the cell
ሶ𝑸𝒓𝒆𝒗 =𝒅
𝒅𝒕𝑻 ∙ ∆𝑺 = 𝑰𝑻
𝒅𝑬𝟎𝒅𝑻
ሶ𝑸𝒊𝒓𝒓𝒆𝒗 =𝒅
𝒅𝒕∆𝑮 +𝑾𝒆𝒍 = 𝑰(𝑬 − 𝑬𝟎)2. “Irreversible” heat rate caused by
Ohmic resistance and polarisation
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP5
EV-ARC: Ø: 25 cmh: 50 cm
ES-ARC: Ø: 10 cmh: 10 cm
Battery Calorimeter (ARC: Accelerating Rate Calorimeter)
EV+ ARC: Ø: 40 cmh: 44 cm
ARC combined with internal or external cycler
= Battery Calorimeter
+
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP6
𝑅𝑡ℎ defined
𝑇𝐶 constant
𝑇𝑆 𝑡 = 𝑇𝑆0 + 𝛼 ∙ 𝑡
𝑻𝑪
𝑻𝑺
𝑅𝑡ℎ very high
𝑇𝐶 = 𝑇𝐶 𝑡= 𝑇𝐶0 + 𝛼 ∙ 𝑡
𝑻𝑪
𝑻𝑺
Battery calorimetry: Accelerating Rate Calorimeter (ARC)
Isoperibolic Adiabatic
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP7
Conversion of thermal data (temperature, temperature rate) to heat (Joule) and power (Watt) with the aim
of understanding of heat release to determine heat removal requirements for thermal management.
To be measured:
Heat generation of the cell during charging and discharging
Key data for thermal management and safety
Methods for the determination of total generated heat
Cell effective specific heat capacity
Heat transfer coefficient
Reversible heat rate
Irreversible heat rate
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP8
Heat generation rate ሶ𝑄𝑔 Heat dissipation rate ሶ𝑄𝑑
Temperaturechange with time
Energy balance for lumped heat transfer system with convective and radiative heat loss
𝑚𝑐𝑝𝑑𝑇
𝑑𝑡= ሶ𝑄𝑔 − ሶ𝑄𝑑
ሶ𝑄𝑑=0
Adiabatic conditions:
ሶ𝑄𝑔 = 𝑚𝑐𝑝𝑑𝑇
𝑑𝑡
Determination of the generated heat
ሶ𝑄𝑑 = 𝐴ℎ ∙ 𝑇𝑆 − 𝑇𝐶 + 𝜀𝜎𝐴 ∙ (𝑇𝑆4 − 𝑇𝐶
4)
Isoperibolic conditions:
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP9
Measurement of the effective specific heat capacity cp
e.g. at 30 °C 𝑐𝑝 = 1.095 ൗ𝐽𝑔 ∙ 𝐾
Sandwich setup for pouch cells
Control of the current applied to the heater mat to ensure a constant heating rate
𝑐𝑝 =∆𝑄
𝑚 ∙ ∆𝑇𝑎𝑑=𝑈 ∙ 𝐼 𝑑𝑡
𝑚 ∙ ∆𝑇𝑎𝑑(4)
m: Mass of the cell
∆𝑇𝑎𝑑: Temperature difference underadiabatic conditions
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP10
Isoperibolic Measurements
Negative temperature coefficient
Discharge parameter:- method: constant current (CC)- Umin = 3,0V- I = 5A → C/8-rate
Charge parameter:- method: constant current,
constant voltage (CCCV)- Umax = 4,1V- I = 5A → C/8-rate- Imin = 0.5A
Pouch cell 40 Ah NMC - GraphiteIdeal conditions→ Single cell
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP11
Discharge parameter:- method: constant current (CC)- Umin = 3,0V- I = 5A → C/8-rate
Charge parameter:- method: constant current,
constant voltage (CCCV)- Umax = 4,1V- I = 5A → C/8-rate- Imin = 0.5A
Adiabatic Measurements
Tst = 23°C (RT)
Adiabatic and Isoperibolic Measurements:
Pouch cell 40Ah NMC - GraphiteWorst Case Conditions→ Cell in a pack surrounded by other cells
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP12
Total cell energy = electrical energy + „chemical“ energy(normal operation) (abuse condition)
Stringfellow, R. et al. “Lithium-Ion Battery Safety Field-Failure Mechanisms.”, 218th ECS Meeting, Las Vegas, 2010.
Energy stored in a cell
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP13
Heat-Wait-Seek Method
Source: Thermal Hazard Technology (THT, 2014)
Example of a Heat-Wait-Seek step.
Thermal Runaway tests
Seek
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP14
0 1000 2000 3000 4000 5000
0
100
200
300
400
500
600
700
800 Samsung_NMC
Sony_LMO
A123_LFP
Te
mp
era
ture
in
°C
Time in min
Thermal Runaway: 18650 cells with different cathode materials
80<T<130°C: low rate reaction, 0.02 - 0.05 °C/min: decomposition of the SEI
100 200 300 400 500 600 700 800
1E-3
0.01
0.1
1
10
100
1000
10000
Samsung_NMC
Sony_LMO
A123_LFP
Te
mp
era
ture
Rate
in
°C
/min
Temperature in °C
130<T<200°C: medium rate reaction, 0.05 - 25 °C/min: anode and electrolyte
=> reduction of electrolyte at negative electrode
T > 200°C: high rate reaction, higher than 25 °C/min: reaction cathode and electrolyte=> rapid generation of oxygen
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP15
Study of ageing effects by thermal runaway tests
0 500 1000 1500 2000 2500
50
100
150
200
250
Tem
pera
ture
in
°C
Time in min
fresh cell
aged cell
80 100 120 140 160 180 200 220 240 260
0.01
0.1
1
10
100
1000
fresh cell
aged cell
Tem
pera
ture
Rate
in
°C
/min
Temperature in °C
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP16
Development of external pressure measurement methods
0 500 1000 1500 2000 2500 3000 3500
0
50
100
150
200
250
300
350
400
450
Temperature
External pressure
Time in min
Tem
pera
ture
in °
C
0
10
20
Ext
erna
l pre
ssur
e in
bar
Safety vent opened
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP17
Internal pressure measurement in 18650 cells
0 500 1000 1500 2000 2500
0
100
200
300
400
500
600
Temperature
Internal pressure
Time in minT
em
pera
ture
in
°C
0
2
4
6
8
10
12
14
Inte
rnal
pre
ssu
re in
bar
Pressure line (Ø 1.5 mm) inside core hole
TC at outer surface
Time delay between Pmax - Tmax
Safety vent opened
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP18
Nail penetration test in the ARC at a 4.5 Ah pouch cell
Nail penetration test on pouch cells in the ARC
-20 -10 0 10 20
50
100
150
200
250
300
350
400
Te
mp
era
ture
in
°C
Time in s
Source: LookKIT 1/2015
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP19
• Extended time for thermal runaway propagation: 9 min
• Improved thermal protection: temperature outside of battery box < 80 °C during thermal runaway
Protective Material evaluation in battery calorimeters:Red: heater mat for thermal runaway initiationGray: protective material for cell 4 and lid of
battery box
Prevention of thermal propagation
0 10 20 30 40 500
200
400
600
800
1000
Tem
pera
ture
in
°C
Time in min
Cell 1
Cell 2
Cell 3
Cell 4
Dt = 9 min
0 10 20 30 40 5020
30
40
50
60
70
80
Tem
pera
ture
on
to
p o
f b
att
ery
bo
x
Time in min
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP20
Summary: Possible measurements with a battery calorimeter
Normal operation
Isoperibolic measurement: constant environmental temperature
Adiabatic measurement: No heat exchange between cell and surrounding area
Measurement of temperature curve and temperature distribution during cycling (full cycles, or application-specific load profiles)
Determination of the generated heat, Separation of heat in reversible and irreversible parts
Abuse conditions
Thermal abuse
External short circuit, nail penetration test
Overcharge, deep discharge
Temperature measurement
External or internal pressure measurement
Gas collection
JRC-Workshop, 8.-9. 3. 2018, Petten, Netherlands KIT, IAM-AWP21
Acknowledgements
This work has been partially funded by the Federal Ministry for Education and Research (BMBF)within the framework “IKT 2020 Research for Innovations” under the grant 16N12515 and issupervised by the Project Management Agency VDI|VDE|IT.
Additional funding by the German Research Foundation priority programme SPP1473 WeNDeLIBis gratefully acknowledged.
Supervised by